Drawing Using Grease Pencil Hotkeys
Hold D and press  LMB to draw
Hold D and press  RMB to erase
Hold &#9096; CtrlD and press  LMB to draw a line
Hold &#9096; CtrlD and press  RMB to draw a poly line


The shortcuts are in the tooltips:



Also note that the Circle select and Grease pencil erase circles are already subtly different:

Circle select Grease pencil